Method for producing aqueous polyurethane dispersions in miniemulsion and in the presence of a catalyst

ABSTRACT

A process for preparing aqueous primary dispersions comprising at least one hydrophobic polyurethane obtainable in miniemulsion by reacting (a) at least one polyisocyanate and (b) at least one compound containing at least one isocyanate-reactive group in the presence of a catalyst.

The present invention relates to a process for preparing aqueouspolyurethane dispersions.

Aqueous polyurethane dispersions (also referred to for short as PUdispersions) and processes for preparing them are common knowledge. Theyare prepared by the acetone process or by the prepolymer mixing process.A disadvantage is that such processes are complicated and expensive,especially if solvents are used. Furthermore the reagents via which thehydrophilic groups are introduced are expensive specialty chemicals. PUdispersions have been used for a long time to coat substrates such asleather, textiles, wood, metal or plastic, for example.

Dispersions can also be prepared from miniemulsions. Miniemulsions arecomposed of water, an oil phase, and one or more surface-activesubstances and have a droplet size of from 5 to 50 nm (microemulsion) orfrom 50 to 500 nm. Miniemulsions are considered to be metastable (P. A.Lovell, M. El-Aasser, Emulsion Polymerization and Emulsion Polymers,John Wiley and Sons, Chichester, N.Y., Weinheim, 1997, pages 700 ff., M.El-Aasser, Advances in Emulsion Polymerization and Latex Technology,30^(th) Annual Short Course, Vol. 3, Jun. 7-11, 1999, Emulsion PolymersInstitute, Lehigh University, Bethlehem, Pa., USA).

The literature discloses numerous processes for preparing aqueousprimary dispersions by free-radical miniemulsion polymerization ofolefinically unsaturated monomers (examples are WO 98/02466, DE-A 196 28143, DE-A 196 28 142, EP-A-401 565, WO 97/49739, EP-A 755 946, and DE-A199 24 674) in which no description is given of the polyaddition ofisocyanates with polyols to give polyurethane.

Dispersions comprising polyurethanes are described for example in Germanlaid-open specification DE-A 198 25 453. WO 00/29465 discloses theuncatalyzed reaction of isocyanate and hydroxyl compounds in aqueousminiemulsions to give polyurethanes.

Also known are polyurethanes without hydrophilic groups, with or withoutsolvents. The disadvantage of such polyurethanes in particular, owing toenvironmental problems, is their use of solvents or free isocyanate.Moreover, they have lower molar masses than the dispersions.

The use of organotin compounds such as dibutyltin dilaurate, forexample, as catalysts for preparing PU dispersions is described in DE-A199 59 653. DE-A 199 17 897 describes a process for producingpolyurethane foams from specific polyetherols using metal saltcatalysts, with potassium salts being used in particular. The earlierGerman patent application with the number 10161156.0 describes thepolyaddition of diisocyanates and diols in the presence of a cesiumsalt. A disadvantage of these processes is that they are carried out viathe intermediate step of preparing a prepolymer.

WO 02/064657 teaches the noncatalytic preparation of aqueouspolyurethane dispersions without the intermediate step of preparing aprepolymer.

It is an object of the present invention to find a process for preparingpolyurethane miniemulsions which does not have the disadvantagesdepicted and which leads to improved PU dispersions. A particular aim isto find a rapid reaction regime which leads to a selectivity increaseand to higher molar masses of the polyurethanes.

We have found that this object is achieved by a process for preparingaqueous primary dispersions comprising at least one hydrophobicpolyurethane obtainable in miniemulsion by reacting at least onepolyisocyanate (a) and at least one compound (b) containing at least oneisocyanate-reactive group, wherein at least one catalyst is added.

The PU dispersions prepared by the process of the invention are quick tosynthesize and are inexpensive, on account of the fact in particularthat there is no preliminary stage of preparing a prepolymer.

For the purposes of the present invention the property of beinghydrophilic describes the constitutional property of a molecule orfunctional group to penetrate the aqueous phase or to remain therein.Correspondingly, a hydrophobic molecule or functional group is one withthe constitutional property of behaving exophilically with respect towater, i.e., of not penetrating water or of departing the aqueous phase.For further details refer to Römpp Lexikon Lacke und Druckfarben, GeorgThieme Verlag, Stuttgart, N.Y., 1998, pages 294 and 295.

The process of the invention finds application in miniemulsionpolymerization to give polyurethanes.

With these processes, generally speaking, in a first step a mixture isprepared from the monomers (a) and (b), the required amount ofemulsifers and/or protective colloid, and also, if desired, hydrophobicaddition and water, and an emulsion is produced from said mixture.

It has been found that the addition of catalysts promotes theurethanization. The addition of hydrophobic catalysts in particularpromotes this process and also suppresses the unwanted side reactionwith water to form urea.

In one preferred version of the process of the invention a mixture isfirst prepared from the monomers (a) and (b), emulsifiers and/orprotective colloids, and, where appropriate, hydrophobic addition andwater. Then an emulsion is produced and is heated with stirring. Whenthe required reaction temperature has been reached the catalyst is addedvia the water phase. With particular preference a hydrophobic catalystis added via the water phase. The water solubility of the hydrophobiccatalyst is preferably ≦1 g/l.

The preferred addition of the preferably hydrophobic catalyst throughthe water phase following dispersion increases the selectivity andraises the molar mass.

Alternatively of course the catalyst can be added to the oil phase ofthe emulsion, i.e., to the monomer phase, before dispersion is carriedout, or can be added to the water phase immediately after the emulsionis prepared. This is followed by heating with stirring.

Suitable catalysts include in principle all catalysts commonly used inpolyurethane chemistry.

Examples of these catalysts include organic amines, especially tertiaryaliphatic, cycloaliphatic or aromatic amines, and/or Lewis-acidicorganometallic compounds. Examples of suitable Lewis-acidicorganometallic compounds include tin compounds, such as tin(II) salts oforganic carboxylic acids, e.g., tin(II) acetate, tin(II) octoate,tin(II) ethylhexoate, and tin(II) laurate, and the dialkyltin(IV) saltsof organic carboxylic acids, e.g., dimethyltin diacetate, dibutyltindiacetate, dibutyltin dibutyrate, dibutyltin bis(2-ethylhexanoate),dibutyltin dilaurate, dibutyltin maleate, dioctyltin dilaurate, anddioctyltin diacetate. Also possible are metal complexes such asacetylacetonates of iron, titanium, aluminum, zirconium, manganese,nickel, and cobalt. Other metal catalysts are described by Blank et al.in Progress in Organic Coatings, 1999, Vol. 35, pages 19-29.

Preferred Lewis-acidic organometallic compounds are dimethyltindiacetate, dibutyltin dibutyrate, dibutyltin bis(2-ethylhexanoate),dibutyltin dilaurate, dioctyltin dilaurate, zirconium acetylacetonate,and zirconium 2,2,6,6-tetramethyl-3,5-heptanedionate.

Bismuth and cobalt catalysts as well, and also cesium salts, can be usedas hydrophobic catalysts. Suitable cesium salts include those compoundsin which the following anions are used: F⁻, Cl⁻, ClO⁻, ClO₃ ⁻, ClO₄ ⁻,Br⁻, I⁻, IO₃ ⁻, CN⁻, OCN⁻, NO₂ ⁻, NO₃ ⁻, HCO₃ ⁻, CO₃ ²⁻, S²⁻, SH⁻, HSO₃⁻, SO₃ ²⁻, HSO₄ ⁻, SO₄ ²⁻, S₂O₂ ²⁻, S₂O₄ ²⁻, S₂O₅ ²⁻, S₂O₆ ²⁻, S₂O₇ ²⁻,S₂O₈ ²⁻, H₂PO₂ ⁻, H₂PO₄ ²⁻, HPO₄ ²⁻, PO₄ ³⁻, P₂O₇ ⁴⁻, (OC_(n)H_(2n+1))⁻,(C_(n)H_(2n−1)O₂)⁻, (C_(n)H_(2n−3)O₂)⁻, and (C_(n+1)H_(2n−2)O₄)²⁻, wheren is a number from 1 to 20.

Preference here is given to cesium carboxylates in which the anion obeysthe formulae (C_(n)H_(2n−1)O₂)⁻ and (C_(n+1)H_(2n−2)O₄)²⁻ with n beingfrom 1 to 20. Particularly preferred cesium salts have monocarboxylateanions of the formula (C_(n)H_(2n−1)O₂)⁻ where n is a number from 1 to20. Here, mention may be made in particular of formate, acetate,propionate, hexanoate, and 2-ethylhexanoate.

Examples of customary organic amines that may be mentioned include thefollowing: triethylamine, 1,4-diazabicyclo[2.2.2]octane, tributylamine,dimethylbenzylamine, N,N,N′,N′-tetramethylethylenediamine,N,N,N′,N′-tetramethylbutanediamine,N,N,N′,N′-tetramethylhexane-1,6-diamine, dimethylcyclohexylamine,dimethyidodecylamine, pentamethyldipropylenetriamine,pentamethyldiethylenetriamine, 3-methyl-6-dimethylamino-3-azapentol,dimethylaminopropylamine, 1,3-bisdimethylaminobutane,bis-(2-dimethylaminoethyl) ether, N-ethylmorpholine, N-methylmorpholine,N-cyclohexylmorpholine, 2-dimethylaminoethoxyethanol,dimethylethanolamine, tetramethylhexamethylenediamine,dimethylamino-N-methylethanolamine, N-methylimidazole,N-formyl-N,N′-dimethylbutylenediamine, N-dimethylaminoethylmorpholine,3,3′-bisdimethylamino-di-n-propylamine and/or 2,2′-dipiperazinediisopropyl ether, dimethylpiperazine,tris-(N,N-dimethylaminopropyl)-s-hexahydrotriazine, imidazoles such as1,2-dimethylimidazole,4-chloro-2,5-dimethyl-1-(N-methylaminoethyl)imidazole,2-aminopropyl-4,5-dimethoxy-1-methylimidazole,1-aminopropyl-2,4,5-tributylimidazole, 1-aminoethyl-4-hexylimidazole,1-aminobutyl-2,5-dimethylimidazole,1-(3-aminopropyl)-2-ethyl-4-methylimidazole, 1-(3-aminopropyl)imidazoleand/or 1-(3-aminopropyl)-2-methylimidazole.

Preferred organic amines are trialkylamines having independently of oneanother two C₁- to C₄ alkyl radicals and one alkyl or cycloalkyl radicalhaving 4 to 20 carbon atoms, examples being dimethyl-C₄-C₁₅-alkylaminessuch as dimethyldodecylamine or dimethyl-C₃-C₈-cycloalkylamine. Likewisepreferred organic amines are bicyclic amines, with or without a furtherheteroatom such as oxygen or nitrogen, such as1,4-diazabicyclo[2.2.2]octane, for example.

It will be appreciated that it is also possible to use mixtures of twoor more of the aforementioned compounds as catalysts.

Particular preference is given to using hydrophobic catalysts from amongthe compounds mentioned.

The catalysts are used preferably in an amount of from 0.0001 to 10% byweight, more preferably in an amount of from 0.001 to 5% by weight,based on the total amount of the monomers used.

Depending on the nature of the catalyst it can be added in solid orliquid form and also in solution. Suitable solvents are water-immisciblesolvents such as aromatic or aliphatic hydrocarbons and also carboxylicesters such as toluene, ethyl acetate, hexane, and cyclohexane, forexample. The catalysts are preferably added in solid or liquid phase.

In one preferred embodiment of the invention the ratio of isocyanategroups (a) to isocyanate-reactive groups (b) is from 0.8:1 to 3:1,preferably from 0.9:1 to 1.5:1, more preferably 1:1.

In accordance with the invention the aqueous dispersions comprisepolyurethanes prepared from polyisocyanates. Suitable polyisocyanates(a) include with preference the diisocyanates commonly used inpolyurethane chemistry.

Particular mention may be made of diisocyanates X(NCO)₂ in which X is analiphatic hydrocarbon radical having 4 to 12 carbon atoms, acycloaliphatic or aromatic hydrocarbon radical having 6 to 15 carbonatoms or an araliphatic hydrocarbon radical having 7 to 15 carbon atoms.Examples of diisocyanates of this kind include tetramethylenediisocyanate, hexamethylene diisocyanate (HDI), dodecamethylenediisocyanate, 1,4-diisocyanatocyclohexane,1-isocyanato-3,5,5-trimethyl-5-isocyanatomethylcyclohexane (IPDI),2,2-bis-(4-isocyanatocyclohexyl)propane, trimethylhexane diisocyanate,1,4-diisocyanatobenzene, 2,4-diisocyanatotoluene,2,6-diisocyanatotoluene, 4,4′-diisocyanatodiphenylmethane,2,4′-diisocyanatodiphenyl-methane, p-xylylene diisocyanate,tetramethylxylylene diisocyanate (TMXDI), the isomers ofbis-(4-isocyanatocyclohexyl)methane (HMDI) such as the trans/trans, thecis/cis, and the cis/trans isomer, and mixtures of these compounds.

Preference is given to using1-isocyanato-3,5,5-trimethyl-5-isocyanatomethyl-cyclohexane (IPDI),tetramethylxylylene diisocyanate (TMXDI), hexamethylene diisocyanate(HDI), and bis-(4-isocyanatocyclohexyl)methane (HMDI).

Diisocyanates of this kind are available commercially.

As mixtures of these isocyanates particular importance attaches to themixtures of the respective structural isomers of diisocyanatotoluene andof diisocyanatodiphenylmethane; the mixture of 80 mol %2,4-diisocyanatotoluene and 20 mol % 2,6 diisocyanatotoluene isparticularly suitable. Also advantageous are the mixtures of aromaticisocyanates such as 2,4-diisocyanatotoluene and/or2,6-diisocyanatotoluene with aliphatic or cycloaliphatic isocyanatessuch as hexamethylene diisocyanate or IPDI, in particular, with thepreferred mixing ratio of the aliphatic to the aromatic isocyanatesbeing from 4:1 to 1:4.

For synthesizing the polyurethanes it is possible to use as compounds(a) apart from the abovementioned isocyanates, those isocyanates whichin addition to the free isocyanate groups carry further, blockedisocyanate groups, e.g., isocyanurate, biuret, urea, allophanate,uretdione or carbodiimide groups.

Examples of suitable isocyanate-reactive groups are hydroxyl, thiol, andprimary and secondary amino groups. Preference is given to usinghydroxyl-containing compounds or monomers as isocyanate-reactivecompounds or monomers (b). Alongside these it is also possible to useamino-containing compounds as monomers (b3).

As compounds or monomers (b) it is preferred to use diols.

With a view to good film forming and elasticity suitable compounds (b)containing isocyanate-reactive groups include primarily diols (b1) ofrelatively high molecular mass, having a molecular weight of from about500 to 5000 g/mol, preferably from about 1000 to 3000 g/mol.

The diols (b1) are, in particular, polyesterpolyols, which are known forexample from Ullmanns Encyklopädie der Technischen Chemie, 4th edition,volume 19, pages 62 to 65. Preference is given to using polyesterpolyolsobtained by reacting dihydric alcohols with dibasic carboxylic acids.Instead of the free polycarboxylic acids it is also possible to use thecorresponding polycarboxylic anhydrides or corresponding polycarboxylicesters of lower alcohols or mixtures thereof to prepare the polyesterpolyols. The polycarboxylic acids can be aliphatic, cycloaliphatic,araliphatic, aromatic or heterocyclic and may have been substituted, byhalogen atoms for example, and/or may be unsaturated. Examples thereofthat may be mentioned include the following: suberic acid, azelaic acid,phthalic acid, isophthalic acid, phthalic anhydride, tetrahydrophthalicanhydride, hexahydrophthalic anhydride, tetrachlorophthalic anhydride,endomethylenetetrahydrophthalic anhydride, glutaric anhydride, maleicacid, maleic anhydride, alkenylsuccinic acid, fumaric acid, and dimericfatty acids. Preferred dicarboxylic acids are those of the formulaHOOC—(CH₂)_(y)—COOH, where y is a number from 1 to 20, preferably aneven number from 2 to 20, examples being succinic acid, adipic acid,sebacic acid, and dodecanedicarboxylic acid.

Examples of suitable diols include ethylene glycol, propane-1,2-diol,propane-1,3-diol, butane-1,3-diol, butane-1,4-diol, butene-1,4-diol,butyne-1,4-diol, pentane-1,5-diol, neopentyl glycol,bis(hydroxymethyl)cyclohexanes such as1,4-bis(hydroxymethyl)-cyclohexane, 2-methylpropane-1,3-diol,methylpentanediols, and also diethylene glycol, triethylene glycol,tetraethylene glycol, polyethylene glycol, dipropylene glycol,polypropylene glycol, and dibutylene glycol and polybutylene glycols.Preferred alcohols are of the formula HO—(CH₂)_(x)—OH where x is anumber from 1 to 20, preferably an even number from 2 to 20. Examples ofsuch alcohols include ethylene glycol, butane-1,4-diol, hexane-1,6-diol,octane-1,8-diol, and dodecane-1,12-diol. Preference extends to neopentylglycol and pentane-1,5-diol. These diols can also be used as diols (b2)directly to synthesize the polyurethanes.

Also suitable, furthermore, are polycarbonate diols (b1), such as may beobtained, for example, by reacting phosgene with an excess of the lowmolecular mass alcohols specified as synthesis components for thepolyester polyols.

Also suitable are lactone-based polyesterdiols (b1), which arehomopolymers or copolymers of lactones, preferably hydroxy-terminatedadducts of lactones with suitable difunctional starter molecules.Suitable lactones include preferably those derived from compounds of theformula HO—(CH₂)_(z)—COOH where z in a number from to 1 to 20 and whereone hydrogen atom of a methylene unit may also have been substituted bya C₁ to C₄-alkyl radical. Examples are ε-caprolactone, β-propiolactone,γ-butyrolactone and/or methyl-ε-caprolactone, and also mixtures thereof.Examples of suitable starter components are the low molecular massdihydric alcohols specified above as a synthesis component for thepolyester polyols. The corresponding polymers of ε-caprolactone areparticularly preferred. Lower polyesterdiols or polyetherdiols as wellcan be used as starters for preparing the lactone polymers. Instead ofthe polymers of lactones it is also possible to use the corresponding,chemically equivalent polycondensates of the hydroxycarboxylic acidscorresponding to the lactones.

Further suitable monomers (b1) include polyetherdiols. These areobtainable in particular by polymerizing ethylene oxide, propyleneoxide, butylene oxide, tetrahydrofuran, styrene oxide or epichlorohydrinwith itself, in the presence of BF₃ for example, or by subjecting thesecompounds, alone or in a mixture or in succession, to addition reactionswith starting components containing reactive hydrogen atoms, such asalcohols or amines, e.g., water, ethylene glycol, propane-1,2-diol,propane-1,3-diol, 1,1-bis-(4-hydroxyphenyl)propane or aniline.Particular preference is given to polytetrahydrofuran with a molecularweight of from 240 to 5000 g/mol, and in particular from 500 to 4500g/mol. In addition it is also possible to use mixtures of polyesterdiolsand polyetherdiols as monomers (b1).

Likewise suitable are polyhydroxyolefins (b1), preferably those having 2terminal hydroxyl groups, e.g., α,ω-dihydroxypolybutadiene,α,ω-dihydroxypolymethacrylic esters or α,ω-dihydroxypolyacrylic esters,as monomers (b1). Such compounds are known for example from EP-A 622378. Further suitable polyols (b1) are polyacetals, polysiloxanes, andalkyd resins.

The hardness and the elasticity modulus of the polyurethanes can beincreased by using as diols (b) not only the relatively high molecularmass diols (b1) but also low molecular mass diols (b2), having amolecular weight of from about 60 to 500 g/mol, preferably from 62 to200 g/mol.

Diols (b2) used include in particular the synthesis components with theshort-chain alkane diols specified for the preparation of polyesterpolyols, with preference being given to the unbranched diols having from2 to 12 carbon atoms and an even number of carbon atoms, and also topentane-1,5-diol and neopentyl glycol. Phenols or bisphenol A or F areadditionally suitable as diols (b2).

The fraction of the diols (b1), based on the total amount of diols (b),is preferably from 0 to 100 mol %, in particular from 10 to 100 mol %,more preferably from 20 to 100 mol %, and the fraction of the monomers(b2), based on the total amount of diols (b), is preferably from 0 to100 mol %, in particular from 0 to 90 mol %, more preferably from 0 to80 mol %. With particular preference the ratio of the diols (b1) to themonomers (b2) is from 1:0 to 0:1, preferably from 1:0 to 1:10, and morepreferably from 1:0 to 1:5.

For components (a) and (b) it is also possible to employ functionalities>2.

Examples of suitable monomers (b3) are hydrazine, hydrazine hydrate,ethylenediamine, propylenediamine, diethylenetriamine,dipropylenetriamine, isophoronediamine, 1,4-cyclohexyldiamine,N-(2-aminoethyl)ethanolamine, and piperazine.

In minor amounts it is also possible to use monofunctionalhydroxyl-containing and/or amino-containing monomers (b3). Theirfraction should not exceed 10 mol %, based on components (a) and (b).

In accordance with the invention the diameters of the monomer dropletsin the emulsion thus prepared are normally <1000 nm, frequently <500 nm.In the normal case the diameter is >40 nm. Preference is givenaccordingly to values of between 40 and 1000 nm. 50-500 nm areparticularly preferred. Especial preference is given to the range from100 nm to 300 nm and the utmost preference to the range from 200 to 300nm.

The emulsion is prepared in conventional manner. The average size of thedroplets of the dispersed phase of the aqueous emulsion can bedetermined in accordance with the principle of quasielastic lightscattering (the z-average droplet diameter dz of the unimodal analysisof the autocorrelation function). This can be done using, for example, aCoulter N3 Plus Particle Analyser from Coulter Scientific Instruments.

The emulsion can be prepared using high-pressure homogenizers forexample. In these machines the fine division of the components isachieved by means of a high local energy input. Two versions have provenparticularly appropriate in this respect:

In the first version the aqueous macroemulsion is compressed to morethan 1000 bar by means of a piston pump, for example, and is thenreleased through a narrow slot. The effect here is based on an interplayof high shear gradients and pressure gradients and cavitation in theslot. One example of a high-pressure homogenizer which operates inaccordance with this principle is the Niro-Soavi high-pressurehomogenizer type NS1001L Panda.

In the case of the second version the compressed aqueous macroemulsionis released into a mixing chamber through two nozzles directed againstone another. In this case the fine distribution effect is dependent inparticular on the hydrodynamic conditions prevailing within the mixingchamber. One example of this type of homogenizer is the Microfluidizertype M 120 E from Microfluidics Corp. In this high-pressure homogenizerthe aqueous macroemulsion is compressed to pressures of up to 1200 barby a pneumatically operated piston pump and is released via what iscalled an “interaction chamber”. Within the “interaction chamber” theemulsion jet is divided, in a microchannnel system, into two jets whichare collided at an angle of 180°. Another example of a homogenizer whichoperates in accordance with this type of homogenization is the NanojetType Expo from Nanojet Engineering GmbH. In the Nanojet, however,instead of a fixed channel system, two homogenizing valves are installedwhich can be adjusted mechanically.

As an alternative to the principles set out above, homogenization mayalso be effected, for example, using ultrasound (e.g., Branson SonifierII 450). The fine distribution here is based on cavitation mechanisms.For homogenization by means of ultrasound the devices described in GB-A22 50 930 and in U.S. Pat. No. 5,108,654 are also suitable in principle.The quality of the aqueous emulsion E1 produced in the sonic fielddepends in this case not only on the sonic input but also on otherfactors, such as the intensity distribution of the ultrasound in themixing chamber, the residence time, the temperature, and the physicalproperties of the substances to be emulsified—for example, theviscosity, surface tension, and vapor pressure. The resulting dropletsize depends, inter alia, on the concentration of the emulsifier and onthe energy introduced during homogenization, and can therefore beadjusted selectively by, for example, altering the homogenizationpressure and/or the corresponding ultrasound energy accordingly.

For the preparation of the emulsion of the invention from conventionalemulsions by means of ultrasound, the device which has provenparticularly suitable is that described in DE-A 197 56 874, which isexpressly included herein by reference.

With particular advantage the means for transferring ultrasound waves isdesigned as a sonotrode whose end remote from the free emitting area iscoupled to an ultrasound transducer. The ultrasound waves may beproduced, for example, by exploiting the inverse piezoelectric effect.In this case generators are used to generate high-frequency electricaloscillations (usually in the range from 10 to 100 kHz, preferablybetween 20 and 40 kHz), and these are converted by a piezoelectrictransducer into mechanical vibrations of the same frequency, and, withthe sonotrode as transfer element, are coupled into the medium that isto be sonicated.

The emulsion can also be prepared by spraying through a nozzle. In thiscase the emulsion is prepared continuously at the rate at which it isconsumed, by the mixing of its components using a mixer apparatus whichhas at least one nozzle, selected from solid cone nozzle, hollow conenozzle, flat jet nozzle, smooth jet nozzle, injector nozzle, ejectornozzle, spiral nozzle, impact jet nozzle, two-fluid nozzle oremulsifying baffle (WO 02/085955).

It is appropriate to prepare the emulsion with sufficient rapidity thatthe emulsifying time is small in comparison to the reaction time of themonomers with one another and with water.

One preferred embodiment of the process of the invention involvespreparing all of the emulsion with cooling to temperatures <RT. Theemulsion is preferably prepared within less than 10 minutes. Thecatalyst is then added and the desired reaction temperature isestablished. The reaction temperatures are between RT and 120° C.,preferably between 50 and 100° C. In another preferred embodiment thehydrophobic catalyst is added through the water phase only after thereaction temperature has been reached.

In another version of the process of the invention first of all theemulsion is prepared from the monomers (a) and (b1) and/or (b2),emulsifiers and/or protective colloids, and also, where appropriate,hydrophobic addition and water, before, once again, the hydrophobiccatalyst is added and the monomers (b3) are added dropwise after thetheoretical NCO content has been reached.

Generally when producing miniemulsions use is made of ionic and/ornonionic emulsifiers and/or protective colloids and/or stabilizers assurface-active compounds.

A detailed description of suitable protective colloids can be found inHouben-Weyl, Methoden der Organischen Chemie, volume XIV/1,Makromolekulare Stoffe [Macromolecular compounds], Georg Thieme Verlag,Stuttgart, 1961, pp. 411 to 420. Suitable emulsifiers include anionic,cationic, and nonionic emulsifiers. As concomitant surface-activesubstances it is preferred to use exclusively emulsifiers, whosemolecular weights, unlike those of the protective colloids, are usuallybelow 2000 g/mol. Where mixtures of surface-active substances are usedit is of course necessary that the individual components are compatiblewith one another, something which in case of doubt can be checked bymeans of a few preliminary tests. Anionic and nonionic emulsifiers arepreferably used as surface-active substances. Customary accompanyingemulsifiers are, for example, ethoxylated fatty alcohols (EO units: 3 to50, alkyl: C₈ to C₃₆), ethoxylated mono-, di-, and tri-alkylphenols (EOunits: 3 to 50, alkyl: C₄ to C₉), alkali metal salts of dialkyl estersof sulfosuccinic acid, and also alkali metal salts and/or ammonium saltsof alkyl sulfates (alkyl: C₈ to C₁₂), of ethoxylated alkanols (EO units:4 to 30, C₉), of alkylsulfonic acids (alkyl: C₁₂ to C₁₈), and ofalkylarylsulfonic acids (alkyl: C₉ to C₁₈).

Suitable emulsifiers can also be found in Houben-Weyl, Methoden derOrganischen Chemie, volume 14/1, Makromolekulare Stoffe, Georg ThiemeVerlag, Stuttgart, 1961, pages 192 to 208.

Examples of emulsifier trade names include Dowfax® 2 A1, Emulan® NP 50,Dextrol® OC 50, Lumiten® N-OP 25, Emulphor® OPS 25, Emulan® OG, Texapon®NSO, Nekanil® 904 S, Lumiten® 1-RA, Lumiten® E 3065, Steinapol NLS, etc.

The amount of emulsifier for preparing the aqueous emulsion isappropriately chosen in accordance with the invention so that in theaqueous emulsion which ultimately results, within the aqueous phase, thecritical micelle concentration of the emulsifiers used is essentiallynot exceeded. Based on the amount of monomers present in the aqueousemulsion this amount of emulsifier is generally in the range from 0.1 to5% by weight. As already mentioned, protective colloids can be added tothe emulsifiers and have the capacity to stabilize the dispersedistribution of the aqueous polymer dispersion which ultimately results.Irrespective of the amount of emulsifier used the protective colloidscan be employed in amounts of up to 50% by weight, for example, inamounts of from 1 to 30% by weight based on the monomers.

As costabilizers it is possible to add to the monomers substances whichhave solubility in water of <5×10⁻⁵ g/l, preferably 5×10⁻⁷ g/l, inamounts of from 0.01 to 10% by weight. Examples are hydrocarbons such ashexadecane, halogenated hydrocarbons, silanes, siloxanes, hydrophobicoils (olive oil), dyes, etc. In their stead it is also possible forblocked polyisocyanates to take on the function of the hydrophobe.

The dispersions of the invention are used for preparing coatingmaterials, adhesives, and sealants. They can also be used for producingfilms or sheets, and also for impregnating, say, textiles.

In the context of their use as coating materials the PU dispersions ofthe invention combine excellent hardness with excellent elasticity. Onflexible substrates toughness and extensibility are ensured. It isadditionally possible to produce materials which achieve excellentthermal stabilities. In the context of use in adhesives the high bondstrength is a further factor.

The examples below are intended to illustrate the invention, thoughwithout restricting it.

The average particle size is determined by quasielastic light scatteringin accordance with ISO 13321 using a Nicomp particle sizer, model 370,on samples at a concentration of 0.01% by weight. The polydispersityMw/Mn, the ratio of the weight-average to the number-average molecularweight, is a measure of the molecular weight distribution of thepolymers and ideally has the value 1. The figures given for thepolydispersity and also for the number-average and weight-averagemolecular weight Mn and Mw relate here to measurements made by gelpermeation chromatography using polystyrene as standard andtetrahydrofuran as eluent. The method is described in AnalytikerTaschenbuch vol. 4, pages 433 to 442, Berlin 1984.

EXAMPLE 1

3.141 g of 1-isocyanato-3,5,5-trimethyl-5-isocyanatomethylcyclohexane(IPDI), 2.859 g of pulverized dodecane-1,12-diol, 200 mg of hexadecane,200 mg of sodium dodecyl sulfate and 24 g of water were stirred togetherat room temperature for 1 hour. The miniemulsion was produced bysonicating with a Branson Sonifier® W-450 (120 s with 90% amplitude inan ice bath). The reaction temperature was then raised to 60° C. and acatalyst was added. The reaction was ended after 4 hours. The resultsare summarized in Table 1. TABLE 1 Particle Poly- Amount of sizedispersity No. Catalyst catalyst [mg] [nm] M_(w) × 10³ index 1 — — 1753.75 1.8 2 DMDA 25 175 3.71 1.8 3 DMTDA 25 165 4.05 1.8 4 DBTDB 25 1753.81 1.8 5 DBTDH 25 165 9.05 2.1 6 DBTL 25 170 7.28 2.1 7 DOTDL 25* 1708.24 2.1 8 DMDA/DBTDL 25/25 160 7.19 2.2*added prior to emulsificationDMDA: dimethyldodecylamineDMTDA: dimethyltin diacetateDBTDB: dibutyltin dibutyrateDBTDH: dibutyltin bis(2-ethylhexanoate)DBTL: dibutyltin dilaurateDOTDL: dioctyltin dilaurate

EXAMPLE 2

18 g of Poly® THF 1000 (BASF Aktiengesellschaft), 0.5 g of hexadecaneand 4 g 1-isocyanato-3,5,5-trimethyl-5-isocyanatomethylcyclohexane weremixed at room temperature and blended with 50 g of fully deionized waterto which 6 g of Steinapol NLS® (Goldschmidt AG) had been added. Themixture was sonicated with a Branson Sonifier® W-450 for 90 s at 100%amplitude and 50% pulse in an ice bath. Thereafter it was heated to 70°C. and stirred at this temperature for 2 h. An IR spectrum of theproduct was recorded, the result being shown in FIG. 1 (graph: “urea”).

Increased formation of urea is apparent as compared with the catalyzedreaction regime (Example 3).

EXAMPLE 3

The experiment from Example 2 was repeated. When the temperature of 70°C. was reached two drops of DBTL were added and the mixture was stirredfor 65 minutes.

An IR spectrum of the product was recorded, the result being shown inFIG. 1 (graph: “urethane”).

Increased formation of polyurethane is apparent as compared with theuncatalyzed reaction regime (Example 2).

1. A process for preparing an aqueous primary dispersion comprising atleast one hydrophobic polyurethane obtained in at least one miniemulsioncomprising reacting (a) at least one polyisocyanate and (b) at least onecompound comprising at least one isocyanate-reactive group in thepresence of at least one catalyst to prepare the aqueous primarydispersion.
 2. The process as claimed in claim 1, wherein (1) a mixtureof the monomers (a) and (b), at least one emulsifier and optionally, atleast one protective colloid, and water is prepared, (2) an emulsion isproduced, (3) the emulsion is heated with stirring, and (4) the catalystis added via the water phase to produce the aqueous primary dispersion.3. The process as claimed in claim 1, wherein the at least one catalystis selected from the group consisting of the classes of the organicamines, Lewis-acidic organometallic compounds, and metal salts, ormixtures thereof.
 4. The process of claim 1, wherein secondary ortertiary aliphatic, cycloaliphatic or aromatic amines are used as the atleast one catalyst.
 5. The process of claim 1, wherein tin(II) ortin(IV) salts of organic carboxylic acids are used as the at least onecatalyst.
 6. The process of claim 1, wherein cesium carboxylates areused as the at least one catalyst.
 7. The process of claim 1, whereindimethyldodecylamine, dimethyltin diacetate, dibutyltin dibutyrate,dibutyltin bis(2-ethylhexanoate), dibutyltin dilaurate, dioctyltindilaurate, zirconium acetylacetonate, zirconium2,2,6,6-tetramethyl-3,5-heptanedionate and optionally, cesiumcarboxylates are used as the at least one catalyst.
 8. The process ofclaim 1, wherein a hydrophobic catalyst is used as the at least onecatalyst.
 9. The process of claim 1, wherein from 0.001 to 5% by weightof catalyst is used, based on the total amount of the monomers used. 10.The process of claim 1, wherein the ratio of component (a) to component(b) is 1:1.
 11. The process of claim 1, wherein component (a) furthercomprises diisocyanates.
 12. The process as claimed in claim 1, wherein1-isocyanato-3,5,5-trimethyl-5-isocyanatomethylcyclohexane (IPDI),tetramethylxylylene diisocyanate (TMXDI), hexamethylene diisocyanate(HDI), and bis-(4-isocyanatocyclohexyl)methane (HMDI) are used as the atleast one polyisocyanate.
 13. The process as claimed in claim 1, whereincomponent (b) further comprises diols.
 14. The process as claimed inclaim 13, wherein, based on the total amount of the diols (b), from 20to 100 mol % of the diols (b1) having a molecular weight of from 60 to500 g/mol and from 0 to 80 mol % of the diols (b2) having a molecularweight of from 500 to 5000 g/mol are used.
 15. The process as claimed inclaim 1, wherein component (b) further comprises at least one compoundcomprising an amine (b3).
 16. The process as claimed in claim 15,wherein, based on components (a) and (b), from 0 to 10 mol % of the atleast one compound comprising an amine (b3) are used.
 17. The process asclaimed in claim 1, wherein the at least one miniemulsion has a monomerdroplet size of from 50 to 500 nm.
 18. The process as claimed in claim1, wherein the at least one miniemulsion has a monomer droplet size offrom 100 to 300 nm.
 19. An aqueous primary dispersion prepared by theprocess of claim
 1. 20. (canceled)
 21. The process as claimed in claim1, wherein (1) a mixture of the monomers (a) and (b), at least oneemulsifier and optionally, at least one protective colloid, and water isprepared, (2) an emulsion is produced, (3) the catalyst is added via thewater phase, and (4) the emulsion is heated with stirring to produce theaqueous primary dispersion.